New Data Demonstrate that 99% of Surveyed Patients Diagnosed With Uveal Melanoma Gain Value From DecisionDx-UM Test

Study Also Shows that Patients’ Decision Regret Levels Do Not Vary According To Low- Or High-Risk DecisionDx-UM Test Result

Castle Biosciences, Inc. (Nasdaq: CSTL), a skin cancer diagnostics company providing personalized genomic information to improve cancer treatment decisions, presented data on its 15-gene expression profile (15-GEP) test, DecisionDx^®-UM, at the Association for Research in Vision and Ophthalmology (ARVO) 2021: Revolutionary Eye and Vision Research Meeting.

The virtual poster is entitled “Uveal Melanoma Patient Attitudes Towards Prognostic Testing Using Gene Expression Profiling.”

DecisionDx-UM, the test highlighted in the poster, is Castle’s prognostic 15-GEP test for patients with uveal melanoma, a rare cancer of the eye that carries a high risk of spreading (metastasizing). The DecisionDx-UM test is designed to accurately identify patients who are at low risk (Class 1) or high risk (Class 2) of metastasis based on the unique biology of their primary tumor and is the current standard of care in the management of uveal melanoma at the majority of U.S. ocular oncology practices.

“Up to half of patients diagnosed with uveal melanoma will experience metastatic disease, and prior studies show that newly diagnosed patients have overwhelmingly been in favor of learning their prognoses,” said first author Basil K. Williams, M.D., assistant professor and director of Ocular Oncology at the University of Cincinnati College of Medicine. “This study demonstrated that uveal melanoma patients were satisfied with their decisions to pursue prognostic information through GEP testing, and they found particular value in DecisionDx-UM’s ability to help them understand their individual metastatic risk.”

Study methods and findings:

• The objective of the patient-based study was to understand uveal melanoma patients’ experiences following testing with DecisionDx-UM compared to patients with alternative or no prognostic testing.
• An online questionnaire was distributed by the Melanoma Research Foundation’s CURE OM (Ocular Melanoma) initiative that captured de-identified information regarding patient-reported experiences. Patients were asked questions regarding the decision to undergo prognostic testing and the extent to which they felt regret about their decisions.
• Of the 177 survey participants, 159 (90%) reported wanting prognostic information at diagnosis.
• Of patients tested with DecisionDx-UM, the vast majority (80/81 respondents, 99%) reported gaining value from their test result, including:
  • Increased knowledge and understanding
  • More personalized treatment options
  • Information relevant to life planning
  • A sense of relief from uncertainty about the future
• Of the patients who received prognostic testing with DecisionDx-UM, decision regret levels did not differ depending on whether they received a low or high-risk test result (Kruskal-Wallis; n=28, 23, 30 for 1A, 1B, 2; p=0.13).
• Patients who received prognostic testing experienced lower levels of decision regret than those who opted out of testing, independent of which prognostic tests were used (Wilcoxon Rank-Sum tests: DecisionDx-UM vs. alternative tests: p=0.89, DecisionDx-UM vs. opt-out: p=0.0002, alternative tests vs. opt-out: p=0.003).

About DecisionDx-UM

DecisionDx-UM is a 15-gene expression profile (GEP) test that uses an individual patient’s tumor biology to predict individual risk of metastasis. DecisionDx-UM is the standard of care in the management of uveal melanoma in the majority of ocular oncology practices in the United States. Since 2009, the American Joint Committee on Cancer (AJCC; v7 and v8) Staging Manual for UM has specifically identified the GEP test as a prognostic factor that is recommended for collection as a part of clinical care. Further, the National Comprehensive Cancer Network (NCCN) guidelines for uveal melanoma include the DecisionDx-UM test result as a prognostic method for determining risk of metastasis and recommended differential surveillance regimens based on a Class 1A, 1B, and 2 result. DecisionDx-UM is the only prognostic test for uveal melanoma that has been validated in prospective, multi-center studies, and it has been shown to be a superior predictor of metastasis compared to other prognostic factors, such as chromosome 3 status, mutational status, AJCC stage and cell type.

It is estimated that nearly 8 in 10 patients diagnosed with uveal melanoma in the U.S. receive the DecisionDx-UM test as part of their diagnostic workup. More information about the test and disease can be found at www.CastleTestInfo.com.

About Castle Biosciences

Castle Biosciences (Nasdaq: CSTL) is a commercial-stage dermatologic cancer company focused on providing physicians and their patients with personalized, clinically actionable genomic information to make more accurate treatment decisions. The Company currently offers tests for patients with cutaneous melanoma (DecisionDx^®-Melanoma, DecisionDx^®-CMSeq), cutaneous squamous cell carcinoma (DecisionDx^®-SCC), suspicious pigmented lesions (DecisionDx^® DiffDx™-Melanoma) and uveal melanoma (DecisionDx^®-UM, DecisionDx^®-PRAME and DecisionDx^®-UMSeq). For more information about Castle’s gene expression profile tests, visit www.CastleTestInfo.com. Castle also has active research and development programs for tests in other dermatologic diseases with high clinical need. Castle Biosciences is based in Friendswood, Texas (Houston), and has laboratory operations in Phoenix, Arizona. For more information, visit www.CastleBiosciences.com.

DecisionDx-Melanoma, DecisionDx-CMSeq, DecisionDx-SCC, DecisionDx DiffDx-Melanoma, DecisionDx-UM, DecisionDx-PRAME and DecisionDx-UMSeq are trademarks of Castle Biosciences, Inc.

Forward-Looking Statements

The information in this press release contains forward-looking statements and information within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended, which are subject to the “safe harbor” created by those sections. These forward-looking statements include, but are not limited to, statements concerning the ability of DecisionDx-UM test results to optimize diagnostic treatment decisions and provide value to patients regarding their diagnoses. The words “anticipates,” “believes,” “estimates,” “expects,” “intends,” “may,” “plans,” “projects,” “will,” “would” and similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words. We may not actually achieve the plans, intentions, or expectations disclosed in our forward-looking statements and you should not place undue reliance on our forward-looking statements. Actual results or events could differ materially from the plans, intentions and expectations disclosed in the forward-looking statements that we make. These forward-looking statements involve risks and uncertainties that could cause our actual results to differ materially from those in the forward-looking statements, including, without limitation, the effects of the COVID-19 pandemic on our business and our efforts to address its impact on our business, subsequent study results and findings that contradict earlier study results and findings, our products’ ability to provide the aforementioned benefits to patients and the risks set forth in our Annual Report on Form 10-K for the year ended December 31, 2020, and in our other filings with the SEC. The forward-looking statements are applicable only as of the date on which they are made, and we do not assume any obligation to update any forward-looking statements, except as may be required by law.

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